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The dorsal nerve cord is one of the embryonic features unique to chordates, along with a notochord and pharyngeal slits. The dorsal nerve cord is a hollow cord dorsal to the notochord. It is formed from a part of the ectoderm that rolls, forming the hollow tube, compared to other animal phyla, which have solid, ventral tubes. The dorsal nerve cord is later modified into the brain and spinal cord.